Photobiology of Epidermal Melanocytes

Abstract

Detecting and responding to sunlight is a basic requirement of nearly all life forms. But how the skin, a principal organ to receive sunlight, precisely detects and responds to light remains poorly understood. Using a combination of live cell imaging, transgenic mouse models, and immunohistochemical analysis, we describe a previously unidentified pathway of photodetection involving the human skin. We show that melanocytes form close contacts with cutaneous nerve fibers, possess molecules that regulate synaptic transmission, and express voltage-gated ion channels. We demonstrate that melanocytes are capable of phototransduction to UV (ultraviolet) light and further demonstrate that this cascade utilizes OPN5, which serves as a direct opsin-based photoreceptor of UV light. This intrinsic UV phototransduction pathway stimulates calcium transients in cultured melanocytes as well as native skin tissue. Our findings suggest that melanocytes possess unexpected sensory functions that constitute a direct pathway that may connect light stimuli to the skin and nervous system. This newly identified skin-neural axis for detecting light may play a role in a range of light-associated conditions ranging from cutaneous sun damage, photosensitivity, and tanning addiction.